Apparatus for purifying waste gases

ABSTRACT

An apparatus for purifying waste gases, particularly waste gases from CVD (chemical vapor deposition), plasma etching or similar processes, with at least one combustion space, which is in a vertical arrangement within an outer pipe and is limited at the top by an umbrella-like cover, and an internally or externally mixing burner, the combustion gas nozzles of which protrude into the combustion space, combustion gas, oxygen or air and waste gas being supplied to the burner, as well as to means for supplying and discharging oxidizing agents and/or absorbents to a scrubbing space above the combustion space. By means of the invention, an apparatus is to be provided for purifying waste gases, which can be manufactured cost-effectively and by means of which the disadvantages of the state of the art are avoided. The invention is characterized in that the burner (12) is fastened centrally in the cover (5), the burner (12) has combustion gas nozzles (13) and at least one waste gas nozzle (14), which are directed vertically downwards into the combustion space (6), and that the reaction products, formed during the combustion process, are passed along the inside of the outer pipe (1) into the scrubbing space (7).

The invention relates to an apparatus for purifying waste gases,particularly waste gases from CVD (chemical vapor deposition), plasmaetching or similar processes, with at least one combustion space, whichis in a vertical arrangement within an outer pipe and is limited at thetop by an umbrella-like cover, and an internally or externally mixingburner, the combustion gas nozzles of which protrude into the combustionspace, combustion gas, oxygen or air and waste gas being supplied to theburner, as well as to means for supplying and discharging oxidizingagents and/or absorbents to a scrubbing space above the combustionspace.

The purification of such waste gases usually takes place in two steps,in that the waste gases initially are combusted and subsequentlypurified in a scrubber. The combustion of the waste gases or theiroxidation takes place in these cases with the help of gas-operatedburners within a combustion chamber.

The EP 0 346 893 B1 discloses such an apparatus for purifying wastegases, which consists of a basic body of circular cross section, whichis essentially closed at the bottom and open at the top. This basic bodyconsists of a cylindrical outer wall and an inner wall, which isdisposed concentrically to the outer wall and forms the boundary of acombustion chamber. A burner for combusting the waste gases, which aresupplied together with the combustion gas to the burner, protrudes frombelow into this basic body into the combustion chamber. At the top, theextent of the combustion chamber is limited by a splash guard, abovewhich, a scrubbing or flushing chamber is located. In this flushingchamber, there is a centrally disposed nozzle, with the help of which aspray cone of a flushing material is produced, with which aerosols andsolids components are flushed out of the combusted waste gas. By meansof the splash guard, the flushing agent is prevented from being sprayedinto the combustion chamber and, with that, onto the burner or into theflame.

The residues, flushed out, are conveyed downwards along the inside ofthe cylindrical outer wall and discharged through a drain the basicbody.

It has proven to be a disadvantage of this apparatus for purifying wastegases that the purification processes of the apparatus itself are veryexpensive and that in particular, there are difficulties with cleaningthe combustion space. In addition, contamination of the combustion gasnozzles and of the waste gas nozzle is almost unavoidable, so thatregular maintenance of the burner is required to assure reliableoperation.

It is therefore an object of the invention to provide an apparatus forpurifying waste gases, which can be manufactured cost-effectively and bymeans of which the disadvantages of the state of the art can be avoided.

This objective is accomplished by an apparatus for purifying waste gasesof the initially mentioned type owing to the fact that the burner isfastened centrally in the cover, that the burner has burner nozzles andat least one nozzle for supplying waste gas, which are directedvertically downward in the combustion space and that the reactionproducts, produced by the combustion process, are passed along theinside of the outer pipe into the scrubbing space, that the basic bodyforms a boundary at the lower end of the combustion space, that, withinthe outer pipe, an inner pipe is provided, which extends as far as intothe basic body and ends at a distance above the bottom of the basicbody, that the reaction products, formed by the combustion process, arepassed along the interior side of the outer pipe from the basic bodyupwards into the scrubbing space and that the absorbent, after it isdispersed in the scrubbing space and enriched with the reactionproducts, is discharged along the inner side of the outer pipe over thebasic body.

With this easily realized apparatus for purifying waste gases, a higheravailability, as well as a significant improvement in the apparatus forpurifying waste gases are attained on the one hand. In particular, aneffect of the combustion process by residues of the combustion, whichare deposited on the burner, in the combustion space or on the interiorside of the outer combustion pipe or at the bottom of the combustionspace, is avoided. A cross sectional constriction of the or a blockageof the combustion gas nozzles, which is otherwise possible, is alsoavoided.

In order to achieve particularly good mixing of the combustion gas withthe waste gas, the burner has several waste gas nozzles, which aresurrounded concentrically by the combustion gas nozzles.

A cooling device is assigned to the burner in order to avoid possibleoverheating. For this purpose, a spraying nozzle for the absorbent andscrubbing agent is disposed within the outer pipe and above the burner.This spraying nozzle, on the one hand, serves for flushing the wastegases emerging from the combustion chamber and, on the other hand, atthe same times cools the housing of the burner. The spray nozzle may beconstructed as a ring nozzle, as a full conical nozzle or as a hollowconical nozzle, so that a sufficient amount of flushing liquid strikesthe housing of the burner.

The ring nozzle is fastened above the cover at the inner wall of theouter pipe. The thereby produced ring of spray is to be directed in thiscase parallel to the inner wall of the outer pipe, as well as againstthe housing of the burner, so that the whole of the cross section withinthe outer pipe is covered.

A significant improvement in the cooling of the burner is achieved whenthe spraying nozzle is connected over a feed line, over which theabsorption or scrubbing agent can be supplied to the spraying nozzle,with a chamber within the burner.

In this way, the burner is cooled internally, so that higher burnertemperatures can be permitted. This construction is thereforeparticularly suitable for hydrogen burners. The chamber should bedisposed between the combustion gas nozzles and the waste gas nozzle,surrounding these concentrically.

In order to avoid excessive heating of the cover and the burner, a heatshield, which surrounds the burner concentrically and expands in thedownwards direction, is disposed between the combustion space and thecover. This heat shield furthermore prevents excessive cooling of thewaste gases, which are to be combusted.

An inner pipe, which surrounds the heat shield, is provided in order toform the side boundary of the combustion space.

An annular gap is formed between the heat shield and the interior wallof the inner pipe. The space between the cover and the heat shield isconnected over openings with the space outside of the outer pipe. Bythese means, and in conjunction with the reduced pressure within thecombustion space, constant flushing of the space between the heat shieldand the cover is achieved.

In a continuation of the invention, a nozzle ring with nozzles, whichare designed for supplying a cleaning agent and directed against theinterior wall of the inner pipe, is disposed in the space between thecover and the heat shield. By these means, it becomes possible, duringthe operating pauses of the apparatus, to clean the combustion spacewith water or an absorbent, without having to open the space for thispurpose.

In order to ensure that the absorbent or flushing agent is dischargedconstantly without interference with the combustion process, the bottomof the basic body is provided at its lowest point with a drain.

The combustion space is terminated at its lower end by a basic body witha conical or a downwardly curved bottom, which is supplied wit a drainat its lowest point. With that, a constant discharge of the absorbent orflushing agent is assured, without having to interfere with thecombustion process.

In order to attain good guidance of the gas and, in particular, todeflect the purified waste gas and pass it into the scrubbing space, theinner pipe protrudes into the basic body and ends at a distance abovethe bottom.

In a special embodiment, the outer pipe and the inner pipe in each caseconsist of an upper part and lower part which are connected detachablyto each other, the basic body being detachably connected with the outerpipe or the lower part of the outer pipe. By these means, a considerablesimplification of the cleaning or maintenance processes is attainedwhich can be improved even further owing to the fact that the upper partof the outer pipe with the burner attached thereto, the cover, the upperpart of the inner pipe, the heat shield, the openings and the nozzlering can be moved axially upward or the basic body can be moved axiallydownward.

In a further variation of the invention, the upper part of the innerpipe has at its lower end a cross-sectional constriction, which forms acircular annular gap with the upper end of the lower part. By thesemeans, an increase in the efficiency of the combustion process isachieved, since a recycling of a portion of the already combusted wastegas is induced therewith and, as a result, the waste gas is suppliedrepeatedly to the combustion process. In addition, a flushing of theinside of the inner pipe and reduction in the amount of the deposits areachieved therewith.

In order to prevent that, in this case, flushing agents or absorbentspenetrate into the combustion space, a protecting pipe, which covers theupper edge of the lower part is disposed between the upper part of theouter pipe and the upper part of the inner pipe.

In a further continuation of the invention, the combustion space isconnected by leadthroughs, in which devices for igniting or monitoringthe burner are disposed, with the space outside of the pipe, or theburner itself contains igniting or monitoring devices.

Between the cover and the inside of the outer pipe, there furthermore isa brush edge, which discharges the flushing agent or absorbent along theinside of the outer pipe and, at the same time, brings about a moreintensive wetting of the waste gas.

Above the cover, the outer pipe is connected over one or more traps toequipment for producing a reduced pressure in the combustion space andin the scrubbing space. By producing the reduced pressure, aspiration ofthe waste gas from the combustion space is achieved on the one hand. Atthe same time, the waste gases are prevented from emerging over theflushing openings and the drain.

The invention will be explained in greater detail in the following bymeans of an example. In the associated drawings,

FIG. 1 shows a diagrammatic, sectional representation of an inventiveapparatus for purifying waste gases,

FIG. 2 shows the apparatus of FIG. 1 with a dividable burner space,

FIG. 3 shows an apparatus for purifying waste gases with recycling ofthe waste gases,

FIG. 4 a simplified apparatus for purifying waste gases without aseparate combustion space,

FIG. 5 shows a diagrammatic, sectional representation of a burner withan additional cooling device,

FIG. 6 shows a sectional representation of a burner that is providedwith combustion gas nozzles and waste gas nozzles and

FIG. 7 shows a plan view of the burner of FIG. 6.

Corresponding to FIG. 1, the apparatus for purifying waste gasesconsists of an outer pipe 1, which is arranged vertically and closed offat its lower end by a basic body 2. The basic body 2 has a bottom 3,which is conical or curved downward and is provided at it lowest pointwith a drain 4.

Within the outer pipe 1, an umbrella-like cover 5 is provided, whichexpands in the downwards direction and divides a lower combustion space6 from a scrubbing space 7 above. The cover 5 is held in the outer pipe1 by connecting elements 9, which are provided with openings 8 and maybe pipe sections, to which the cover 5 is fastened. In order to permitthe passage of gas from the combustion space 6 to the scrubbing space 7,the diameter of the cover 5 is less then the internal diameter of theouter pipe 1. As a result, an annular gap 10 is kept free in the regionof the inner wall of the outer pipe 1 and covered by a brush edge 11fastened to the cover 5.

Furthermore, a burner 12, with downwardly pointing combustion gas andnozzle 13 and waste gas feeding nozzle 14, is fastened centrally in theumbrella-like cover 5. The burner 12 can be fastened to the cover 5 byscrews or bolts or by a clamping ring. In order to obtain good mixing ofthe waste gas, which is supplied through the waste gas feeding nozzle14, with the combustion gas, the waste gas feeding nozzle 14 isconstructed as a central nozzle, which is surrounded by an annularcombustion gas nozzle 13 or by several combustion gas nozzles 13. Ascombustion gas, natural gas in particular, which is combusted with anexcess of oxygen, or hydrogen, which is also combusted with an excess ofoxygen, comes into consideration.

Below the cover 5, there is a heat shield 15, which surrounds the burner12 and the combustion gas and waste gas feeding nozzles 13, 14, expandsconically downwards and is used, in particular, for reducing the heatload on the cover 5. An internal pipe 16, which is fastened to the cover5 and surrounds the heat shield 15, extends downwards from the cover 5to form the boundary of the combustion space 6. Moreover, an annular gap17 is kept free between the heat shield 15 and the interior wall of theinner pipe 16, so that the space between the cover 5 and the heat shield15 is connected through openings 8 with the space outside of the outerpipe 1. By these means, flushing of the space between the cover 5 andthe heat shield 15 is attained, when there is a reduced pressure in thecombustion space 6.

The inner pipe 16, which extends up into the basic body, serves at thesame time to separate the flame in the combustion space 6 from the wastegases, which are added in the thermal reaction region and which arepassed as reaction gases from the basic body 2 to the inside of theouter pipe 1 upwards into the scrubbing space 7.

In the scrubbing space 7 above the burner 12, there is a spray nozzle 18for supplying an absorbent and dividing it very finely or producing verysmall droplets of it. This absorbent serves for washing out the gaseousor solid reaction products formed curing the combustion of the wastegas. The spraying cone of the spray nozzle 18 is constructed as a fullcone and extends up to the inside of the outer pipe 1. At the same time,cooling of the burner 12 is achieved in this manner.

The absorbent is dispersed uniformly in the scrubbing space 7 by thespray nozzle 18 and subsequently passed through the cover 5 and thethereto attached brush edge 11 to the inside of the outer pipe and flowsfrom there into the basic body 2 and over the drain 4 into a collector,which is not shown.

For cleaning the inside of the inner pipe 16, there is, at the upper endof this pipe 16 at the cover 5, a nozzle ring 19, with which water or anabsorbent can be sprayed onto the inside of the inner pipe 16 duringpauses in the operation, so that so that deposits there can be removedor reduced.

The scrubbing space 7 is closed off al the top by a trap 20 forretaining solid or liquid aerosols. The tap is connected with an exhaustinstallation, which at the same time produces the required reducedpressure.

For igniting the burner flame and for monitoring the combustion process,a leadthrough 21 extends from the outer pipe 1 through the cover 5 intothe heat shield 15. A pilot light and/or a UV flame sensor may bedisposed in the leadthrough.

FIG 2 basically shows the apparatus for purifying waste gases, the outerand inner pipes 1, 16 being constructed in divided form so that theapparatus can be disassembled and maintained particularly easily. Theouter pipe 1 comprises for this purpose an upper and a lower part 1a, 1band the inner pipe 16 comprises an upper and a lower part 16a, 16b,which in each case are detachably connected to one another. In addition,the basic body 2 may be detachably connected with the outer pipe 1 orwith the lower part 1a of the outer pipe 1.

The upper part 1a of the outer pipe 1, to which the burner 12 isattached, with the cover 5, with the upper part 16a of the inner pipe16, with the heat shield 15, with the openings 8 and the nozzle ring 20,can also be constructed so that it can be moved axially upwards or thebasic body 2 can be constructed so that it can be moved axiallydownwards. As a result, the combustion space 6 can be cleanedparticularly easily.

FIG. 3 shows a special variation of the invention, for which internalrecycling of the waste gas and internal flushing of the inner pipe 16 isrealized. Fundamentally the construction corresponds to that of thevariation shown in FIG. 2, the upper part 16a of the inner pipe 16having at the lower end a cross sectional constriction 22, which isconcentric with the lower part 16b and protrudes into it. Parts of thewaste gas, passed upwards through the annular gap 23 so formed betweenthe lower part 16b and the inside of the lower part 1b, are suppliedonce again to the combustion space 6 and exposed once again there to thehot flame. Furthermore, by means of this recycling, flushing of theinside of the lower part 16b is attained, so that deposition ofparticles is prevented at least partially there.

A protective pipe 24, which covers the upper edge of the lower part 16b,is located between the upper part 1a of the outer pipe 1 and the upperpart 16a, in order to prevent penetration of absorbent through theannular gap 23 into the combustion space.

By means of this protective pipe 24, excessive cooling of the upper partof the combustion space 6 is prevented at the same time.

FIG. 4 shows a simplified variation of the invention, for which thecombustion space 6 is surrounded only by the outer pipe 1. In order toattain better cooling of the burner 12 here, the absorbent is suppliedto the spray nozzle 18 over the burner 12, in that the feed line 25 ispassed into the housing of the burner, as explained in the following.

A particularly effective variation for cooling the burner 12 is evidentfrom FIG. 5. For this variation, a chamber 26, which surrounds the wastegas nozzle 14 concentrically, is disposed between the waste gas nozzle14 and the combustion gas nozzle or nozzles 13. This chamber 26 isconnected on the one hand, over a pipeline 27 with the spray nozzle 18and, on the other, with a device for feeding the flushing agent orabsorbent. In this way, a particularly intensive cooling of the burneris achieved without any effect on the temperature of the combustionprocess itself. With this, the variation is suitable particularly forhydrogen burners or for combustion processes having a highertemperature.

FIGS. 6, 7 show an arrangement for the simultaneous combustion of wastegases from different processes. As can be seen from FIG. 6, two wastegas nozzles 14, 14' are disposed directly adjacent to the burner 12 forthis variation, the waste gases being supplied over separate gas-feedingsystems 29, 29'. The combustion gas nozzles 13 surround the waste gasnozzles 14, 14' and are supplied over a combustion gas feeding system,which is not shown, over an annular compensating chamber 30. Anadditional oxygen-supplying system 29 ensures a combustion with aparticularly high excess of oxygen.

By means of this arrangement, the simultaneous combustion of wastegases, which would react in an uncontrolled manner with one anotheroutside of the combustion chamber, becomes possible. As a result, asignificantly more effective utilization of the apparatus for thepurification of waste gases is achieved at the same time.

Basically, the number of waste gas supplying systems 29, 29' is notlimited, the number of waste gas nozzles 14, 14' being limited only bythe size of the burner 12. For reliable operation with several waste gassupplying systems, it is merely necessary to ensure that the waste gasis reliably prevented from flowing back into the waste gas supplyingsystems 29, 29'.

List of Reference Symbols

1 outer pipe

1a upper part

1b lower part

2 basic body

3 bottom

4 drain

5 cover

6 combustion space

7 scrubbing space

8 opening

9 connection element

10 gap

11 brush edge

12 burner

13 combustion gas nozzle

14 waste gas nozzle

15 heat shield

16 inner pipe

16a upper part

16b lower part

17 annular gap

18 spray nozzle

19 nozzle ring

20 trap

21 leadthrough

22 cross sectional constriction

23 annular gap

24 protective pipe

25 feed line

26 chamber

27 pipeline

28 oxygen supplying system

29 waste gas supplying system

30 compensation chamber

We claim:
 1. An apparatus for purifying waste gases, particularly wastegases from CVD (chemical vapor deposition), plasma etching or similarprocesses, with at least one combustion space, which is in a verticalarrangement within an outer pipe and is limited at the top by anumbrella-like cover, and an internally or externally mixing burner, thecombustion gas nozzles of which protrude into the combustion space,combustion gas, oxygen or air and waste gas being supplied to theburner, as well as to means for supplying and discharging oxidizingagents and/or absorbents to a scrubbing space above the combustionspace, characterized in that the burner (12) is fastened centrally inthe cover (5), the burner (12) has combustion gas nozzles (13) and atleast one waste gas nozzle (14), which are directed vertically downwardsinto the combustion space (6), in that the combusiton space (6) isbounded at the lower end by a basic body (2), in that, within the outerpipe (1), an inner pipe (16) is provided, which extends as far as intothe basic body (2) and ends at a distance above the bottom (3) of thebasic body (2), in that the reaction products, formed during thecombustion process, are passed along the inside of the outer pipe (1)from the basic body (2) upwards into the scrubbing space (7) and in thatthe absorbent, after being dispersed in the scrubbing space (7) andenriched with reaction products, is discharged along the interior sideof the outer pipe (1) over the basic body (2).
 2. The apparatus of claim1, characterized in that the combustion gas feeding nozzles (13)surround the waste gas nozzles (14) concentrically.
 3. The apparatus ofclaims 1 or 2, characterized in that a cooling device is assigned to theburner (12).
 4. The apparatus of one of the claims 1 or 2, characterizedthat, within the outer pipe (1) and above the burner (12), a spraynozzle (18) for the absorbent or scrubbing agent is disposed, which isconstructed as a ring nozzle, a full conical nozzle or a hollow conicalnozzle.
 5. The apparatus of claim 4, characterized in that the spraynozzle (18) is connected with a chamber (26) within the burner (12) overa pipeline (27), over which the absorbent or scrubbing agent can besupplied to the spray nozzle (18).
 6. The apparatus of claim 5,characterized in that the chamber (26) is disposed between thecombustion gas feeding nozzles (13) and the waste gas nozzle (14) andsurrounds these concentrically.
 7. The apparatus of claims 1 or 2,characterized in that a heat shield (15), which surrounds the burner(12) concentrically and expands downwards, is disposed between thecombustion space (6) and the cover (5).
 8. The apparatus of claim 7,characterized in that an inner pipe (16) is provided within the outerpipe (1), extends from the cover (5) downwards and surrounds the heatshield (15).
 9. The apparatus of claim 8, characterized in that anannular gap (17) is formed between the heat shield (15) and the internalwall of the inner pipe (16) and in that the space between the cover (5)and the heat shield (15) is connected through openings (8) with thespace outside of the outer pipe (1).
 10. The apparatus of one of theclaim 7, characterized in that a nozzle ring (19), with nozzles forsupplying a purifying agent, which are directed against the interiorwall of the inner pipe (16), is disposed in the space between the cover(5) and the heat shield (15).
 11. The apparatus of claim 1 or 2,characterized in that the bottom (3) of the basic body (2) is providedat its lowest point with a drain (4).
 12. The apparatus of claim 1 or 2,characterized in that the outer pipe (1) and the inner pipe (16) in eachcase consist of an upper part (1a, 16a) and a lower part (1b, 16b),which are detachably connected with one another.
 13. The apparatus ofclaim 12, characterized in that the basic body (2) is detachablyconnected with the outer pipe (1) or the part (1b) of the outer pipe(1).
 14. The apparatus of claim 12, characterized in that the upper part(1a) of the outer pipe (1), together with the cover (5) and the theretoattached burner (12), and the upper part (16a) of the inner pipe (16),can be moved axially upwards.
 15. The apparatus of claim 12,characterized in that the basic body (2) can be moved axially downwards.16. The apparatus of claim 17, characterized in that the upper part(16a) of the inner pipe (16) has at its lower end a cross sectionalconstriction (22) which, together with the upper end of the lower part(16b), forms an annular gap (23).
 17. The apparatus of claim 16,characterized in that a protective pipe (24), the upper edge of whichcovers the lower part (16b), is disposed between the upper part (1a) ofthe outer pipe (1) and the upper part (16a) of the inner pipe (16). 18.The apparatus of claims 1 or 2, characterized in that the combustionspace (6) is connected by leadthroughs (21) with the space outside ofthe pipe (1) and in that devices for igniting or monitoring the burner(12) are disposed in the leadthroughs (21).
 19. The apparatus of claims1 or 2, characterized in that the burner (12) contains devices for itsignition and monitoring.
 20. The apparatus of claims 1 or 2,characterized in that there is a brush edge (11) between the cover (5)and the inside of the outer pipe (1).
 21. The apparatus of claims 1 or2, characterized in that the outer pipe (1) is connected above the cover(5) with one or several traps (20) to equipment for producing a reducedpressure in the combustion space (6) and in the scrubbing space (7).